[ Thanks to Steven J.
Vaughan-Nichols for this link. ]
“As a recent Slashdot reader found out, many ISPs won’t
let you run your own mail server. Specifically they block port 25,
the Simple Mail Transfer Protocol (SMTP) port, which is used for
sending mail. If you can’t send mail, there’s not much point in
having a mail server.“While some Slashdot readers were outraged by this, there’s
nothing new here. Comcast, AT&T, and Cox to name but a few
ISPs, block port 25 as a matter of course and they’ve done it for
years. Why? As one person put it, “Most ISPs block outgoing port 25
because 99.99% of that traffic is viruses or otherwise malicious
computers trying to send spam. Even more mail services block all
dynamic pools used by major ISPs because of the same reason.””